Method and apparatus for implementing spatial division multiple access ("SDMA") to communicate user data and backhaul data with the same wireless time-frequency resources

TECHNICAL FIELD

p-0002This invention relates generally to the use of the same wireless time-frequency resources for both communicating both user data and backhaul data via SDMA.

BACKGROUND

p-0003Mobile communications networks typically utilize a plurality of base stations to connect user terminals to a wireless network. Each of the user terminals communicates with a base station to exchange information with the wireless network when located in a cell area serviced by the base station. The base station transmits backhaul data back and forth with a core network via a backhaul link.

p-0004The transmission of backhaul data via wired connections is expensive and can cause delay in wireless development. Wireless backhaul, on the other hand, typically uses separate time/frequency resources from those of the wireless data such as, e.g., an alternate system offering services on a different bandwidth allocation. These separate resources, however, may not be available or offer an acceptable range/quality such as, e.g., unlicensed spectrum.

p-0005There are systems in the art in which communication on the same time-frequency resources can be achieved via spatial separation with an antenna array, a practice known as Spatial Division Multiple Access (“SDMA”). In SDMA, an antenna array forms multiple spatial channels to allow several communication links to share the same time frequency resources. A receive antenna array employs multiple receive beamformers, each arranged to receive one communication link, while spatially suppressing the other communication links. Similarly, a transmit antenna array employs multiple transmit beamformers, each arranged to transmit one communication link towards its intended recipient while transmitting it away from other receivers through transmit spatial nulling.

p-0006There are wireless backhaul systems in the art that handle the use of backhaul communications by using backhaul repeaters in communication with one or more base stations to forward backhaul communications from the base station(s) to a backhaul access point, and the multiple backhaul links share the same time frequency resources via the practice of SDMA. These systems, however, utilize separate frequency resources for backhaul and for normal wireless data communications. In cellular systems in the initial phase of deployment, such backhaul systems may not be usable because the separate time-frequency resources may not be available.

p-0007There are wireless cellular systems in the art that employ SDMA to enable multiple wireless data communication links between wireless users and a base station to share the same time-frequency resources. However, the backhaul traffic for these systems is either handled with wired links (which can prevent rapid network deployment) or use wireless backhaul links on a different spectral allocations (which in some cases might be unavailable) or steal time-frequency resources from the wireless data traffic (which severely reduces network efficiency). Accordingly, current wireless systems are complex and inefficient.

BRIEF DESCRIPTION OF THE DRAWINGS

p-0008The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention.

p-0009<figref idrefs="DRAWINGS">FIG. 1</figref> illustrates a wireless system according to an embodiment of the invention;

p-0010<figref idrefs="DRAWINGS">FIG. 2</figref> illustrates a data frame according to an embodiment of the invention; and

p-0011<figref idrefs="DRAWINGS">FIG. 3</figref> illustrates a method of simultaneously communicating wireless data and wireless backhaul data according to an embodiment of the invention.

p-0012Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of various embodiments of the present invention. Also, common and well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.

DETAILED DESCRIPTION

p-0013Generally speaking, pursuant to these various embodiments, a method and system are provided that utilize the same time and frequency resources to simultaneously transmit both backhaul data and user terminal data directly from a base station to a backhaul access point and user terminals. Spatial Division Multiple Access (“SDMA”) is utilized for this communication. According to this method and system, neither separate time or frequency resources, nor a dedicated carrier are required. By utilizing the same time and frequency resources an efficient multiplexing of backhaul data and user terminal data is achieved.

p-0014SDMA is the practice of using array-processing techniques to permit multiple users of a wireless system to share the same time and frequency resources. In SDMA systems, users are multiplexed in the spatial domain instead of in the code domain as is done in Code Division Multiple Access (“CDMA”). Therefore, no additional bandwidth is required for SDMA other than that required for channel estimation, link maintenance, and so forth. SDMA systems may be generally described in the context of an antenna array operating at a base station that is communicating with multiple single-antenna subscriber devices.

p-0015<figref idrefs="DRAWINGS">FIG. 1</figref> illustrates a wireless system <b>100</b> according to an embodiment of the invention. As shown, the wireless system <b>100</b> includes a base station <b>105</b>. The base station <b>105</b> has a processor <b>110</b>, a memory <b>115</b>, and a transceiver <b>120</b>. The transceiver <b>120</b> may comprise an antenna array operating in a transmit mode and/or receive mode. The memory <b>115</b> may store programmable program code to be executed by the processor <b>110</b>. The transceiver <b>120</b> may communicate wireless data with a first user terminal <b>125</b>, a second user terminal <b>130</b>, and a third user terminal <b>132</b> within cell <b>134</b>. The first user terminal <b>125</b>, the second user terminal <b>130</b>, and the third user terminal <b>132</b> may each comprise, e.g., a cellular telephone or other wireless platform of choice. The transceiver <b>120</b> is also utilized to communicate wireless backhaul data to a central backhaul point <b>135</b>.

p-0016Although not illustrated, additional base stations may also be in communication with the central backhaul point <b>135</b>. The central backhaul point <b>135</b> may, in turn, be in communication with a core network <b>140</b>. The communication link between the central backhaul point <b>135</b> and the core network <b>140</b> may comprise, e.g., a hard-wired link. When a call is made on, e.g., the first user terminal <b>125</b>, wireless data is transmitted to the transceiver <b>120</b>. The base station <b>105</b> then wirelessly transmits corresponding backhaul data to the central backhaul point <b>135</b> via the transceiver <b>120</b>. The central backhaul point <b>135</b> subsequently transmits the backhaul data to the core network <b>140</b> which may route the appropriate data to a base station servicing the corresponding user terminal being called.

p-0017This base station <b>105</b> and its antenna array <b>120</b> communicate in both the downlink direction (transmit) and the uplink (receive) direction. For example, communications in the downlink direction may include communications of wireless data from the base station <b>105</b> to any of the first user terminal <b>125</b>, the second user terminal <b>130</b>, or the third user terminal <b>132</b>, as well as communications of backhaul data to the central backhaul point <b>135</b>. In the uplink direction, wireless data may be transmitted from the first user terminal <b>125</b>, the second user terminal <b>130</b>, or the third user terminal <b>132</b> to the base station <b>105</b> as well as communications of backhaul data from the central backhaul point <b>135</b>.

p-0018Backhaul data may also be transmitted in the uplink direction from the central backhaul point <b>135</b> to the base station <b>105</b>. In the uplink direction, multiple user terminals such as the first user terminal <b>125</b>, the second user terminal <b>130</b>, and the third user terminal <b>132</b> may transmit wireless data to the base station <b>105</b> on the same time-frequency resources as those utilized for transmitting backhaul data from the central backhaul point <b>135</b> to the base station <b>105</b>. The base station <b>105</b> uses receive SDMA processing techniques to separate the transmissions based on the distinct vector channel responses of the transmitting user terminals and the central backhaul point <b>135</b> relative to the antenna array within the base station's <b>105</b> transceiver <b>120</b>.

p-0019Backhaul data may also be transmitted in the downlink direction from the base station <b>105</b> to the central backhaul point <b>135</b>. In the downlink direction, the base station may use transmit SDMA to transmit wireless data to multiple user terminals such as the first user terminal <b>125</b>, the second user terminal <b>130</b>, and the third user terminal <b>132</b> on the same time-frequency resources as those utilized for transmitting backhaul data from the base station <b>105</b> to the central backhaul point <b>135</b>. In downlink transmit SDMA, multiple independent data signals are beam-formed with a transmit array in such a way as to form non-interfering spatial channels between the transmit array and the central backhaul point <b>135</b> and each user terminal such as, e.g., the first user terminal <b>125</b>, the second user terminal <b>130</b>, and the third user terminal <b>132</b>.

p-0020The processor <b>110</b> of the base station <b>105</b> generates an SDMA data frame. The SDMA data frame includes both the backhaul data and wireless user data. The processor <b>110</b> generates the SDMA frame such that both the backhaul data the wireless user data are transmitted as efficiently as possible. The amount of backhaul data needed may vary on a frame-by-frame basis depending on system conditions. For the best statistical multiplexing, all of the time-frequency resources in a frame are available for normal data communications. The amount of backhaul required is calculated by the processor <b>110</b>, and a fraction of a frame is allocated for the backhaul such as, e.g., the first ⅓ of a frame from the beginning. After the portion of the frame is allocated for backhaul, the wireless user data is added to the frame. For example, in the downlink direction, the same subcarriers and Orthogonal Frequency-Division Multiplexing (“OFDM”) symbols may be utilized to simultaneously transmit both the backhaul data and the wireless user data via SDMA. This may occur in certain circumstances such as when the central backhaul point <b>135</b> and a user terminal with which the base station is communicating have channel responses that enable the transmit SDMA beamforming operations to create spatial channels that are sufficiently separated, such that there is substantially no interference or cross-talk in the communication of the respective backhaul data and wireless user data between these distinct entities.

p-0021<figref idrefs="DRAWINGS">FIG. 2</figref> illustrates a data frame <b>200</b> according to an embodiment of the invention. The data frame <b>200</b> includes a plurality of subcarriers and a plurality of OFDM symbols. As discussed above, the data frame <b>200</b> is portioned into two portions. A first portion <b>205</b> of the data frame <b>200</b> includes SDMA wireless backhaul data and wireless user data. A second portion <b>210</b> of the data frame <b>200</b> includes wireless user data only, i.e., there is no wireless backhaul data in the second portion <b>210</b>. Note that the first portion <b>205</b> does not necessarily have to encompass OFDM symbols that are earlier than the symbols allocated to the second portion. Similarly, the first portion <b>205</b> does not necessarily have to encompass all subcarriers of the OFDM symbols. In some embodiments, the first portion occupies a “rectangle” of OFDM subcarriers and symbols. In another embodiment, the first portion can occupy a set of disjoint subcarriers and symbols.

p-0022User data is selected for the backhaul portion of the data frame <b>200</b> such that SDMA communication may be made with the first user terminal <b>125</b>, the second user terminal <b>130</b>, or the third user terminal <b>132</b> and with the central backhaul point <b>135</b> at the same time with the same frequency resources. If the angular location (or more specifically the vector channel responses) of a user terminal and the central backhaul point <b>135</b> are similar, however, and SDMA performance would suffer from the inability to adequately separate the user terminal, then that user terminal may be scheduled for the second portion <b>205</b> of the data frame <b>200</b>, i.e., the non-backhaul portion.

p-0023In an embodiment, only the 2-dimensional angle is considered and wireless user data is overlapped with the backhaul data only if the user terminals' transmissions are in substantially opposite directions (e.g., substantially different directions) of the central backhaul point <b>135</b>. Referring to <figref idrefs="DRAWINGS">FIG. 1</figref>, the central backhaul point <b>135</b> and each of the first user terminal <b>125</b> and the second user terminal <b>130</b> are located in substantially opposite directions. The third user terminal <b>132</b> and the central backhaul point <b>135</b> are not, however, located in substantially opposite directions. Instead, the third user terminal <b>132</b> and the central backhaul point <b>135</b> are located in relatively close proximity to each other. As a result, if backhaul data were to be sent from the base station <b>105</b> at the same time that wireless user data is sent from the base station <b>105</b> to the third user terminal <b>132</b>, interference between the transmitted signals could result, interrupting or degrading system performance.

p-0024Accordingly, wireless data to be sent to either the first user terminal <b>125</b> or the second user terminal <b>130</b> may be located within the same portion, i.e., the first portion <b>205</b>, of the data frame <b>200</b> having backhaul data to be sent to the central backhaul point <b>135</b>. Wireless user data to be sent to the third user terminal <b>132</b>, on the other hand, would be included only in the part of the data frame <b>200</b> having only wireless user data and no backhaul data, i.e., the second portion <b>210</b>, to ensure the most reliable communication of such data.

p-0025<figref idrefs="DRAWINGS">FIG. 3</figref> illustrates a method of simultaneously communicating wireless data and wireless backhaul data according to an embodiment of the invention. To begin, at operation <b>250</b>, as discussed above, the processor <b>110</b> of the base station <b>105</b> determines whether any wireless user data and/or backhaul data is to be communicated. Next, at operation <b>255</b>, the processor <b>110</b> determines the location information of the central backhaul point <b>135</b> relative to any serviced user terminals with which the base station <b>105</b> is to communicate wireless user data. For example, the base station <b>105</b> may be in communication with the first user terminal <b>125</b>, the second user terminal <b>130</b>, and the third user terminal <b>132</b>. The location determination is made at operation <b>255</b> so that the processor <b>110</b> can determine which wireless user data may be communicated via SDMA at the same time as backhaul data without resulting in interference. For example, the location determination may be angular location or vector channel responses of a user terminal and the central backhaul point <b>135</b>.

p-0026Next, at operation <b>260</b>, the processor <b>110</b> generates the first portion <b>205</b> of a data frame <b>200</b> having both the backhaul data and the wireless data. The same time and frequency resources are utilized to transmit/receive both the wireless user data and the backhaul data within the first portion <b>205</b> of the data frame <b>200</b>. For example, the base station <b>105</b> may include wireless user data to be communicated with the first user terminal <b>125</b> and/or the second user terminal <b>130</b> in the first portion <b>205</b>, along with the backhaul data. Next, at operation <b>265</b>, the processor <b>110</b> generates the second portion <b>210</b> of the data frame <b>200</b>. The second portion <b>210</b> may include only wireless user data. For example, the second portion <b>210</b> may include wireless user data to be communicated between the base station <b>105</b> and the third user terminal <b>132</b>. The wireless user data to be communicated with the third user terminal <b>132</b> is included in this second portion <b>210</b>, i.e., the non-backhaul portion, because it is likely that interference would result if this wireless user data were transmitted at the same time as the backhaul data because of the close proximity of the central backhaul point <b>135</b> and the third user terminal <b>132</b>. Finally, at operation <b>270</b>, the data frame <b>200</b> is communicated. For example, on a downlink communication, the data frame <b>200</b> is transmitted by the transceiver <b>120</b> of the base station <b>105</b>. Conversely, on an uplink communication, the data frame <b>200</b> is received by the transceiver <b>120</b> of the base station <b>105</b>.

p-0027In certain propagation environments, specifically those with a high amount of multipath scattering, the angular locations of the user terminal and/or a central backhaul point may not affect significantly SDMA performance. In those environments, the operation <b>255</b> of determining the locations is not necessary, and is therefore not performed. In such an embodiment, the flow from operation <b>250</b> in <figref idrefs="DRAWINGS">FIG. 3</figref> proceeds directly to operation <b>260</b>. Other criteria, such as information on pending traffic, can then be used to determine which transmissions will be scheduled in the first portion and which transmissions will be scheduled in the second portion.

p-0028As discussed above, the wireless user data and the backhaul data are communicated via OFDM symbols. The allocation of the wireless user data and the backhaul data may be performed on a frame-to-frame basis such that the relative sizes of the first portion <b>205</b> and the second portion <b>210</b> may change from frame-to-frame based on wireless backhaul data needs. The first portion <b>205</b> and the second portion <b>210</b> of the data frame <b>200</b> may be contiguous sets of OFDM symbols. When a user terminal is rapidly moving through a cell <b>134</b> serviced by the base station <b>105</b>, the processor <b>110</b> of the base station <b>105</b> may keep the wireless user data to be transmitted to the moving user terminal separate from the backhaul data even though the user terminal is not currently too close to the central backhaul point <b>135</b> such that interference with the transmission of backhaul data would likely result. The reason why this user data would be allocated this way is because as the user terminal moves through the cell the processor <b>110</b> may determine that there is a likelihood that interference might soon result based on the user terminal's movement. In making this determination, the processor <b>110</b> may consider the user terminal's velocity and/or direction of movement. For example when the moving user terminal's velocity and a Doppler measurement (or a measurement of the channel response variability or how rapidly the channel response varies) of the user terminal exceed a preset threshold, its user data may be allocated solely to the second portion <b>210</b>, i.e., the non-backhaul portion, of the data frame <b>200</b>. The user data may also be allocated to the second portion <b>210</b> when the user terminal is near an edge of the base station's <b>105</b> communication range. A user terminal for which only the second portion <b>210</b> of the data frame <b>200</b> is to be used may also be assigned a low modulation and coding rate.

p-0029Pursuant to these various embodiments described above, a method and system are provided that utilize the same time and frequency resources to simultaneously transmit both backhaul data and user data directly from a base station to a central backhaul point and user terminals. SDMA is utilized for this communication. According to this method and system, neither separate time or frequency resources, nor a dedicated carrier are required for the backhaul traffic. By utilizing the same time and frequency resources, a good multiplexing of backhaul and user data is achieved.

p-0030Those skilled in the art will recognize that a wide variety of modifications, alterations, and combinations can be made with respect to the above described embodiments without departing from the spirit and scope of the invention, and that such modifications, alterations, and combinations are to be viewed as being within the ambit of the inventive concept.